Kaleya river catchment regional estimation of reservoir capacities using sonar and gis approaches

Small reservoirs in arid and semi-arid areas help rural communities to cope with prolonged dry spells. More recently, the construction and operation of small reservoirs has resulted in upstream versus downstream water use conflicts in some river basins. In this regard, bathymetric information could be used as a tool to monitor the available surface water, and minimize or prevent water conflicts. The challenge is that it is difficult to survey a large number of reservoirs using the traditional sounding methods. Despite the availability of new methods of conducting bathymetric surveys, their utilization in Africa is still low, particularly for depth measurements of small reservoirs. This paper presents modern bathymetric survey and analysis techniques applied for quantifying the capacities of small reservoirs, using the case of the Kaleya River Basin in southern Zambia. The objectives of the survey were to: i) create a database of reservoir storage capacities; and ii) introduce an efficient modern approach of monitoring small reservoir storage capacities. A remote controlled Coden hydrographic survey boat equipped with a SONAR device mounted with Trimble OmniSTAR VBS providing DGPS was used to capture and record hydrographic (xyz) data with greater accuracy. Data analysis was done using Surfer 13 Golden software to produce ten contoured bathymetric maps of surveyed reservoirs. From this information, the reservoir capacities were computed, thus providing information on water stored in reservoirs in the basin. It is concluded that the quantification of storage capacity of small reservoirs using SONAR and GIS provides a quicker and cost effective way of obtaining accurate bathymetric data. Such data is important in resolving water use conflicts in river basins and for decision-making in the context of multiple water uses, climate change and or variability.